In these days, various methods of using a finite element (FE) model obtained by dividing a pneumatic tire (hereinafter, referred to as tire) into a plurality of finite elements to predict tire properties including tire durability for designing a tire based on the predicted tire properties have been proposed.
Any of those methods uses a computer to prepare a finite element model. The prepared finite element model is used to reproduce a desired static state or dynamic state. Then, a mechanical physical quantity in the reproduced state is calculated to evaluate tire characteristics. As a result, a tire sectional shape of the finite element model excellent in tire properties can be obtained, thereby enabling efficient tire designing.
For example, the following Patent Documents 1 to 3 disclose a method of analyzing a desired tire property of a pneumatic tire. Based on the analyzed tire property, a tire can be designed.
JP 2000-141509 A discloses tire designing based on tire performance through a fluid, such as drainability, performance on snow and noise performance, using a tire model according to a finite element method.
JP 11-201874 A discloses a simulation method of predicting a vibration characteristic of a tire by using a tire model according to a finite element method.
JP 2002-99579 A discloses a method of calculating a fluctuation error in characteristics such as durability of a target object such as a tire when a variation in a manufacturing process or a component member or a fluctuation in usage conditions or the like occurs. By using the result of calculation, a design proposal exhibiting stable performance is obtained.
On the other hand, JP 2002-192924 A discloses a method of defining a margin of safety by using a breaking strain, a breaking stress or a breaking strain energy density, which is proper to a material of a tire component member, so that the result of a durability simulation of a tire according to finite element analysis of the tire is identical with the actual result of the durability of the tire, thereby designing a tire excellent in durability.
Although tires actually manufactured by the above-described methods have a desired tire property, the tire property changes with the use of the tire to be completely different from that in an initial state in many cases. Moreover, even if the tire property is good in the initial state, the tire property is sometimes greatly degraded with use.
Such a change in tire properties is due to a change of a tire shape with time, which is caused depending on usage conditions or a use environment of the tire. For example, an outer diameter of a tire is increased to change a sectional shape of the tire. Specifically, the tire properties are greatly affected by a change in tire profile shape (tire sectional shape), which is caused by a change with time with the use of the tire. In particular, the durability is greatly affected by the tire profile shape that constantly changes with the use of the tire.
In conventional techniques including the above-mentioned Patent Documents, however, a tire profile shape change with time, which is caused by the use of the tire, cannot be predicted by using the finite element model to calculate a mechanical physical quantity of the durability after a change with time. Therefore, a tire excellent in durability cannot be designed in consideration of a change of a tire with time.
Accordingly, the present invention has an object to provide a tire designing method of predicting a tire profile shape change with time, which is caused by the use of a tire, by using a tire model to allow a tire excellent in durability to be designed and a program for executing the designing method.